FEATURE
A NEW FORMULA
FOR FIGHTING URBAN OZONE "Cleaner"
gasolines designed to reduce ozone go on sale this month, but how effective will they be in improving urban air quality?
B
eginning this year, gasoline sold in many parts of the United States will have a different formula than in the past, thanks to new federal regulations designed to curb urban ozone (the main ingredient of smog) and reduce toxic air pollutants from auto exhaust. The new reformulated gasoline (RFG) mandated by EPA will cost oil refiners billions of dollars to produce—as much as five cents per gallon. Nine metropolitan areas with severe ozone problems—Los Angeles, New York, Baltimore, Philadelphia, Chicago, Milwaukee, Houston, San Diego, and Hartford, CT—are required to sell the new gasoline during the summer. Approximately 80 more areas with less severe problems also can opt into the RFG program as a way to satisfy federal requirements for curbing their ozone levels. If all these cities opt in, approximately half of all the gasoline sold nationwide would be RFG. Although this "cleaner" gasoline will reduce emissions of certain air toxics and compounds that lead to the formation of ozone, the jury is still out as to how effective federal RFGs will be in improving air quality, especially ozone. William Chameides of the Georgia Institute of Technology voices a view typical of atmospheric scientists when he says the effects of RFGs on urban ozone will be "modest at best. They're certainly not going to solve the problem." Indeed, five years after the passage of the law mandating their use, "there's not universal agreement on what the impacts of these gasolines will be," says Chameides. Ozone is the nation's most pervasive air pollution problem, according to EPA (i). An estimated 44.6 million people live in coun-
TONY
REICHHARDT
3 6 A • VOL. 29, NO. 1, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
0013-936X/95/0929-36A$09.00/0 © 1994 American Chemical Society
Reformulated gasoline on sale in 1995 Cities required to use federally mandated Phase I reformulated gasoline to reduce ozone and states with cities or areas that have chosen to participate in the RFG program (as of Oct. 1995)
Los Angeles San Diego
ties that do not meet the National Ambient Air Qual ity Standards for ozone; 14.3 million people live in counties that do not meet such standards carbon monoxide. The RFG rule is one of the many mandates of the Clean Air Act Amendments of 1990, the monumen tal legislation that imposed a wide array of new reg ulations on cars, fuels, and industry. Section 211(k)(l) of the A m e n d m e n t s ordered EPA to publish— within one year of the Act's passage—regulations that would "require the greatest reduction in emissions of ozone forming volatile organic compounds (dur ing the high ozone season) and emissions of toxic air pollutants (during the entire year) achievable through the reformulation of conventional gasoline," while considering other factors such as cost and energy re quirements.
Congressional formula The Clean Air Act set two key "performance" tar gets for RFG: a 15% reduction (compared to 1990 lev els) in emissions of ozone-forming volatile organic compounds (VOCs) and a 15% reduction in air tox ics such as benzene. Congress also mandated that re formulated gas cause no increase in oxides of nitro gen (NOx), which interact with VOCs in the presence of sunlight to form ozone. Along with these performance standards, Con α: gress threw in additional, specific requirements that CL· amounted to a prescription for RFG: it must con Ο Ο ο tain a maximum of 1% benzene and a minimum of g 2% oxygen by weight. These "Phase I" require LU ο ments take effect this month. Ι Ο Phase II for RFG, which comes into play in Janχ
ary 2000, sets stricter standards for toxics and VOC emissions: each must come down by at least 25% from the 1990 baseline. The law gave EPA the dis cretion to set the final standard as low as 20%, how ever, depending on feasibility and cost. It is this Phase II fuel that maximizes current fuel research on re ducing emissions, although the reformulation re quires more time for refiners to implement. Following the law's passage in 1990, EPA began to craft detailed regulations based on these general guidelines. After a long process that included con sultation with the automobile, oil, environmental, and other affected communities in a regulatory negoti ation ("reg neg") process, the agency issued its fi nal RFG rule last lune (2). The reg neg process itself had a significant im pact on the shape of the final rule and included "a lot of compromises" on both sides, according to Blakeman Early of the Sierra Club, who partici pated in the negotiations. Among the most impor tant concessions to the oil companies, he says, was to allow fuels to be certified as legal RFG through computer models rather than through testing. Al though environmental groups would have pre ferred actual testing, the refiners claimed this would be too expensive. At the time, EPA was developing the so-called "complex model," which would allow a simulated test: a refiner could plug its fuel formula into one end of the computer model and out would come a predic tion of exhaust emissions, which could then be used to determine compliance with the law. The com plex model wasn't quite ready in 1991, however. Be cause the Act required that refiners have four years
Q_
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Impact of fuel changes on exhaust emissions Regulated pollutants such as h y d r o c a r b o n s , c a r b o n m o n o x i d e , N O x , and airborne toxics can be reduced by changes in the c o m p o s i t i o n of a u t o m o t i v e f u e l , according t o an extensive study by the Auto/Oil Quality I m p r o v e m e n t Research P r o g r a m (3) Hydrocarbons
Carbon monoxide
-15 -20 -25 NS= Not significant -30 Fuels were tested on 1989 model vehicles. Reid vapor pressure reduced from 9 psi to 8 psi. Aromatics reduced from 45% to 20%. Oxygenate used was 15% methyl-fert-butyl ether. Olefins reduced from 20% to 5%. 90% distillation temperature (Tgo) reduced from 360 °F to 280 °F. Sulfur reduced from 450 ppm to 50 ppm.
to develop RFG before the 1995 Phase I deadline, the reg neg parties agreed that a less sophisticated "simple model" could be used as a stopgap measure until 1998, when the complex model would have to be used.
Emissions research With that rule in place, the oil industry turned to the task of reformulating gasoline, using methods identified by such research efforts as the Air Quality Improvement Research Program (AQIRP), also known as the Auto/Oil study (3) (see sidebar "Baseline Research. .."). Begun in 1989, AQIRP was created by 14 oil companies and Chrysler, Ford, and General Motors. The $40 million research project has produced extensive data on vehicle emissions and modeling studies of ozone formation. One relatively simple and cost-effective way to cut VOC emissions is to lower the Reid vapor pressure (RVP) of the gasoline, which makes it less likely to evaporate. Evaporative emissions account for 32% of total VOC emissions, according to EPA estimates. Results from the Auto/Oil study show that lowering RVP by only one pound per square inch (psi), from 9 psi to 8 psi, can bring exhaust VOC emissions down 4% and total evaporative emissions down 34%. For Phase I of the RFG regulations, EPA has established even lower guidelines for RVP—between 7.1 and 8 psi, depending on the region—in the summertime, when evaporative emissions are a bigger problem. The Auto/Oil study identified three other fuel composition changes as being promising for reducing ozone: lowering T90 (the distillation temperature at which 90% of the fuel evaporates), reducing its olefin content, and lowering fuel sulfur. For cost reasons, though, sulfur reduction is expected to play a larger part in Phase II (post-2000) gasoline reformu3 8 A • VOL. 29, NO. 1, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
lation. According to the Auto/Oil study, the incremental manufacturing cost of reducing sulfur to 50 ppm is only 2.1 to 4.6 additional cents per gallon, versus 5 to 8.8 cents for reducing T90 to 280 °E if each parameter is controlled individually. Reducing sulfur in gasoline benefits practically every category of emission, because sulfur prevents the pollutants from being catalyzed. The Auto/Oil study found that lowering sulfur from 450 parts per million (ppm) to 50 ppm reduced VOC emissions by 18%, carbon monoxide by 19%, air toxics by 10%, and NOx by 8% in current vehicles. Despite the Clean Air Act's focus on controlling VOC emissions to reduce urban ozone, scientists have paid at least as much attention in recent years to the role of NO x in ozone formation. A 1991 report by the National Research Council (4), for example, said that VOC control alone is of minimal benefit to reducing ozone in certain cities. EPA has stated that NO x reduction is an effective ozone control strategy for northeastern cities and, in some areas, limiting NO x alone may be enough to solve the problem. The specific targeting of VOCs by Congress was outdated scientific thinking even by 1990— "something the policy makers did," according to Harvey leffries, an ozone modeler at the University of North Carolina. At the time, however, the role of NO x was less understood, and there was even concern that reducing it might cause urban ozone levels to rise in certain cases. Although the Clean Air Act Amendments did not require EPA to reduce NO x emissions from gasoline, the turning tide of scientific opinion regarding its importance in ozone formation caused the Agency to act anyway. Phase II RFG will require 6.8% lower NO x emissions. This can be accomplished cost effectively, says EPA, by lowering sulfur from a 1990
baseline level of 339 ppm to about 140 ppm. EPA also has imposed new NO-,, control standards on vehi cles themselves, beginning with 1994 models. California, meanwhile, has made ΝΟ χ reduction a centerpiece of its own RFC program, which be gins in March 1996. These highly prescriptive regu lations call for, among other things, a maximum av erage sulfur content of 30 ppm, which will decrease NO^ emissions by an estimated 15%.
The value of oxygenates The requirement to add oxygenates to RFG has been the most controversial part of the new regulations. Adding oxygen to gasoline is an accepted way to re duce carbon monoxide (CO) emissions, which are known to have detrimental health effects. The most common fuel oxygenates are ethanol (derived mostly from corn), methanol (a petroleum product), and two ethers: ETBE (ethyl-iert-butyl ether) and MTBE (methyl-rerf-butyl ether). Unlike urban ozone, which is primarily a sum mertime problem, CO pollution is more severe dur ing the winter. So EPA has instituted a separate win tertime oxygenated fuel program, mandated by a different section of the Clean Air Act. The winter time "oxy fuels" program began in 36 U.S. cities in 1992. This program requires the addition of 2.7% ox ygen by weight in wintertime gasoline. The new RFG rules, however, require 2% oxygen by weight be cause higher levels of some oxygenates can drive up evaporative VOC emissions in the summer. Beyond limiting CO emissions, oxygenates have little advantage. In a comprehensive July 1993 pa per in Science on controlling vehicle emissions (5), J. G. Calvert, John Seinfeld (chair of the 1991 Na tional Research Council study on urban ozone), and their co-authors stated that oxygenates "appear to of fer negligible benefits in terms of decreasing atmo spheric ozone formation. No convincing argument based on combustion or atmospheric chemistry can be made for the addition of ethanol to gasoline." The authors went on to say that congressional require ments for oxygenates in the Clean Air Act Amend ments of 1990 were "arbitrary, in a scientific sense," considering that there was little quantitative infor mation at the time on the relation between fuel com position and emissions. Why, then, was a requirement for oxygenates writ ten into the RFG section of the Clean Air Act amend ments, which are primarily targeted at summer time ozone, not wintertime CO? Politics played some role. According to the Sierra Club's Early, it was part of a strategy to build a coalition that would ensure passage of the Act. "We had the opportunity, by put ting the oxygenate requirement in [the RFG sec tion] , to get the support of those members who were responsive to the corn and ethanol industry, as well as members who might be influenced by the MTBE manufacturers," he says. There continues, however, to be a debate as to whether oxygenates could actually raise NO x emis sions, which would put one provision of the RFG rules in conflict with another. When EPA was preparing its "simple model," the agency acknowledged that add ing oxygenates to gasoline might drive up NO^ emis
sions (2). But according to the EPA rule on RFG pub lished last February, "Under the final complex m o d e l . . . oxygen has been found to result in no NOx increase, in fact, it results in a very slight decrease." The rule went on to say, though, that as a result of other changes that occur to the fuel when oxy genates are added, "there is no assurance under the simple model that oxygenate addition will not in crease NO^ emissions. The more oxygenate add ed . . . the greater the possibility for a NO x in crease. For this reason EPA believes it is still appropriate to cap the maximum oxygen content un der the simple model at 2.7%. Any higher oxygen con centrations will require use of the complex model." Refiners are required to use the complex model in 1998. The Auto/Oil study also found that oxygenates could pose a problem, driving up NO x by as much as 5% in low-aromatic fuels (which reduce air tox ics). In addition, "splash b l e n d i n g " ethanol— mixing it in tanks during truck transport—was seen to increase light-duty vehicle contribution to ozone because of increased vapor pressure and evapora tive emissions.
California's RFG Perhaps the biggest challenge to EPAs assessment of the NO x risk from oxygenates has come from Cali fornia. According to the California Air Resources Board predictive model, which is similar in intent to EPA's complex model, oxygen levels above 2% by weight result in NOx increases (6). Why the discrepancy between California's assess-
Oxygenates on trial Originally, EPA's rule for RFG was designed to be "fuel neutral" with regard to oxygenates—it did not specify what kind of oxygenate a refiner would have to use as long as the gasoline included 2% oxy gen by weight. Most refiners would probably choose in that case to use MTBE, a petroleum product, instead of ethanol products de rived from corn. But in December 1993, in a move widely considered to be moti vated by the Clinton administration's desire to appease farm belt politicians, EPA revealed that it was mandating a 30% market share for "renewable" oxygenates such as ethanol and ETBE in RFG. In the face of subsequent criticism from the oil industry and environ mental groups, EPA agreed last summer to a phase-in in which only 15% of the market share would go to renewables in 1995, with 30% required in the following year. EPA officials during congressional hearings last year admitted that there are no environmental benefits to favoring ethanol over methanol. They spoke instead of the importance of developing re newable fuel sources and of decreasing U.S. dependence on im ported oil. Privately, some EPA officials say they don't agree with the ethanol mandate and wouldn't mind if the American Petroleum Institute wins its lawsuit challenging the rule. That challenge already has had some success: In September the U.S. Court of Appeals for the District of Columbia ruled that EPA would have to stay the 15% ethanol requirement until after the law suit is decided. The 30% mandate may never take effect if, as many involved in the debate expect, the government loses its case in court. —TONY REICHHARDT
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ment of the risks from oxygenates and EPA's? Per haps it's just a difference in modeling methodol ogy, according to David Korotney of EPA's Fuel Studies and Standards Branch in Ann Arbor, MI. "The big ca veat on all this process is that with statistics, there are no hard and fast rules," he says. Although 2% oxygenate satisfies the require ment for RFG, the wintertime oxy fuel level of 2.7% is higher than what California's predictive model deems safe for NOx emissions. So, under a clause of the Clean Air Act that allows states a waiver if they can show that adhering to one part of the law would lead to increases in other pollutants, California has asked permission to cap oxygen content at 2% yearround. EPA has not yet acted on the request. There is also a dollar cost to adding oxygenates to RFG. A recent Department of Energy analysis (7) shows that if a refiner were to reformulate gas for Phase II RFG with only ozone reduction in mind and no oxygenate requirement, it would be 40% cheaper than manufacturing federally mandated RFG. Ac cording to the analysis, Gulf Coast state refineries, which produce half of U.S. gasoline, could control NOx and VOCs (by reducing sulfur, olefins, and low ering RVP) for an additional 3.8 cents per gallon, ver sus the additional 6.7 cents a gallon it will cost to also add oxygenates and remove air toxics to satisfy the RFG regulations. Even though states with ozone "nonattainment" areas could probably find a cheaper way to refor mulate fuel to solve their ozone problems, most of the large northeastern states and Texas have al ready opted into the federal RFG program. One rea son is mat under federal laws, the states have to dem onstrate to EPA that they have a viable plan for controlling ozone. If a state sets its own standards for reformulated gas, it also must devote time and money to a testing program to monitor compliance. By sim ply opting into the federal RFG rules, the state buys into an already sanctioned method of showing com pliance. According to an EPA official, "This is an easy one for the states, because the gasoline marketers take care of everything." Predicting ozone levels An even more fundamental question regarding RFG is whether it will be effective in reducing urban ozone. Some atmospheric scientists remain skeptical. Jef fries, in fact, questions one of the basic premises be hind the RFG approach. He recently completed more than two years of smog-chamber experiments (β) sponsored by the Coordinating Research Council (a cooperative effort of auto and oil companies) to de termine whether current models can accurately pre dict a rise or fall in urban ozone levels based on changes to individual fuel ingredients. "And the an swer is, they can't," he says. Existing models don't ac count for all the complex conditions of weather and different mixtures of chemical species in the atmo sphere required to create ozone, which change from place to place and from moment to moment. Still, atmospheric scientists generally agree that the key tofightingurban ozone probably lies in low ering NOx. However, this has to be done on a re gional rather than a city-by-city basis, and it will only
work if larger sources such as power plants are re duced as well. Says Chameides, "The amount of ozone that's pro duced is ultimately determined by how much NOx there is. The VOCs determine how fast it's pro duced. So ultimately, we're going to have to address the NO^. problem." Many members of the environmental commu nity accept RFG in the spirit of "something is better than nothing"—a political victory if not a cure-all for urban ozone. Early concedes that "At the time we were legislating, the benefits [of RFG] appeared to be greater than what they might appear to be now." But he and others also defend it as having real shortterm and long-term benefits, particularly when used with future "clean car" technology also mandated by the Act. Most of the real improvement in automo bile air pollution over the next decade will in fact come from these clean cars rather than from RFG alone. By early in the next century, tailpipe emis sion standards are expected to be so low that the au tomobile's contribution to urban ozone will be min imal. RFG will play a role because the cleanerburning cars also will require cleaner fuels. Early also points out that RFG is one of the few provisions of the Clean Air Act related to automo bile pollution that has not become stalled since the Act was passed in 1990. "So many of the other pieces that everybody hoped would help contribute to the solution are not happening," he says, including fed eralized auto inspection and maintenance pro grams and wider limitations on vehicle miles trav eled by one-driver cars. This leaves RFG, imperfect as it is, as one of the few programs that will actually go into effect as planned and on schedule. "Be cause other parts of the Clean Air Act aren't work ing as we hoped," says Early, "RFG is becoming more and more important." References (1) Environmental Protection Agency. National Air Quality and Emissions Trends Report, 1992; Office of Air Quality Plan ning and Standards: Research Triangle Park, NC, Oct. 1993; EPA454/R-93-031. (2) Environmental Protection Agency. 59 Fed. Regist. 7716, Feb. 16, 1994. (3) "Phase 1 Final Report. Auto/Oil Air Quality Improve ment Research Program (AQIRP)"; May 1993. (4) National Research Council. Rethinking the Ozone Prob lem in Urban and Regional Air Pollution; National Acad emy Press: Washington, DC, 1991. (5) Calvert, J. G. et al. Science 1993, 261, 37-45. (6) California Air Resources Board. Staff Report, California Phase 2 Reformulated Gasoline Specifications, Vol. 2: Pro posed Regulation for California Wintertime Oxygenates Pro gram; Los Angeles, CA: Oct 1991, p. 20. (7) McNutt, B. Office of Energy Demand Policy. U.S. Depart ment of Energy. "Economic Impact of Reformulated Gas oline Requirements in PADD I and PADD III Refineries"; presented at Symposium on Impact of Reformulated Fu els, American Chemical Society annual meeting, Wash ington, DC, Aug. 1994. (8) Jeffries, H.; Sexton, K. "The Relative Ozone-Forming Po tential of Methanol Fuel Vehicle Emissions and Gasoline Fuel Vehicle Emissions in Outdoor Smog Chambers"; in terim report; Coordinating Research Council Project ME-1; Feb. 1993. Tony Reichhardt is a freelance science journalist and ed itor based in Washington, DC. VOL.29, NO. 1, 1995/ENVIRONMENTAL SCIENCE & TECHNOLOGY • 4 1 A
